Spirometry pattern classification (obstructive vs restrictive vs mixed) from FEV1/FVC and lung volumes
Core concept
- Read the ratio first, then the volumes. Always in that order.
| Pattern | FEV1/FVC | FVC | TLC | Confirm with |
|---|---|---|---|---|
| Obstructive | dec | Normal or dec | Normal or inc | Bronchodilator response, lung volumes |
| Restrictive | Normal or inc | dec | dec | TLC is mandatory |
| Mixed | dec | dec | dec | TLC below LLN despite obstruction |
| Normal / early restriction | inc with normal FEV1 and FVC | Normal | Normal | Often a normal young person |
- *A low FVC alone is NOT restriction* - air trapping in severe obstruction lowers FVC as much as fibrosis does
- Restriction is defined by a reduced TLC, measured by plethysmography, dilution or washout
- The threshold has moved
- Use the lower limit of normal (LLN), i.e. z-score < -1.645, for both the ratio and the volumes
- A fixed FEV1/FVC <0.70 overdiagnoses obstruction in the elderly and underdiagnoses it in the young (the ratio falls physiologically with age)
- GOLD still uses post-bronchodilator FEV1/FVC <0.70 for COPD - the two coexist and both appear in exams
- GLI reference equations, race-neutral (GLI Global), are the current standard
3 more sections, plus exam facts
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